Alloy 625 vs Alloy 718: A Comprehensive Comparison

Shaanxi Shangyou Stainless Steel Co., Ltd. supplies both Nickel Alloy 625 (UNS N06625) and Nickel Alloy 718 (UNS N07718) in plate, sheet, round bar, seamless pipe, and forging forms. As two of the most widely used nickel-based superalloys, they serve fundamentally different purposes. Alloy 625 is a solid-solution strengthened alloy prized for outstanding corrosion resistance across a wide range of aggressive environments. Alloy 718 is a precipitation-hardenable alloy designed for exceptionally high strength at elevated temperatures. The choice between them hinges on whether corrosion resistance or mechanical strength is the primary design driver. Both alloys are available with EN 10204 3.1 MTC, PMI testing, and full traceability .

Alloy 625 derives its strength from solid solution strengthening – molybdenum and niobium atoms dissolved in the nickel-chromium matrix distort the crystal lattice, impeding dislocation movement . The alloy cannot be age-hardened to significantly higher strength levels. This simplicity is an operational advantage: 625 retains excellent ductility and can be welded and used in the as-welded condition without post-weld heat treatment .

Alloy 718 is precipitation hardened through additions of niobium, aluminum, and titanium . During aging heat treatment at 620-720°C, these elements form gamma-double-prime (γ'') and gamma-prime (γ') precipitates that act as powerful barriers to dislocation motion . This aging response enables 718 to achieve tensile strengths above 1,240 MPa – roughly double that of 625 . However, this strength comes at a cost: the γ'' precipitates coarsen and transform to delta phase above approximately 650°C, causing strength loss .

• Alloy 625 provides excellent strength for a solid-solution alloy: yield strength ~414 MPa, tensile strength ~827 MPa .
• Alloy 718 delivers exceptional precipitation-hardened strength: yield strength > 1,000 MPa, tensile strength > 1,240 MPa .

• Alloy 625 exhibits greater elongation (30% minimum), making it more forgiving in forming operations .
• Alloy 718 has lower elongation (12% minimum) due to its precipitation-hardened microstructure but retains good toughness .

• Alloy 625 maintains useful strength and oxidation resistance up to approximately 980°C .
• Alloy 718 is limited to approximately 650-700°C for sustained service because the strengthening precipitates degrade above this temperature .

Alloy 625 has superior corrosion resistance in virtually all environments :

• Pitting and Crevice: 625 exhibits exceptional resistance in seawater (PREN > 50); 718 provides good but not equivalent performance .
• Chloride SCC: Both alloys resist chloride stress-corrosion cracking, but 625 is the more proven choice for severe service .
• Acid Environments: 625 withstands reducing and oxidizing acids simultaneously (HCl, H₂SO₄, HF); 718 has adequate but lower acid resistance .
• High-Temperature Oxidation: 625 is superior up to higher temperatures due to higher chromium content .

Alloy 718 is generally less expensive than Alloy 625 due to its higher iron content and lower molybdenum content . Material costs are approximately :

• Alloy 625: ~USD 40-60 per kg
• Alloy 718: ~USD 30-50 per kg

Choose Alloy 625 when:

• Corrosion resistance is the primary concern (seawater, acids, chlorides)
• Service temperature exceeds 650°C
• Weldability and as-welded service are important
• The application requires excellent pitting and crevice corrosion resistance

Choose Alloy 718 when:

• High strength (above 1,000 MPa yield) is required
• Service temperature is below 650°C
• Creep and fatigue resistance at elevated temperatures are critical
• The application is a high-stress rotating component or fastener

For a detailed quotation or material selection assistance, please provide:

For corrosive service, also provide:

• Request Alloy 625 Quote
• Request Alloy 718 Quote
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The fundamental difference is the strengthening mechanism. Alloy 625 is solid-solution strengthened for outstanding corrosion resistance. Alloy 718 is precipitation-hardened for exceptionally high mechanical strength.

Alloy 625 has superior corrosion resistance in virtually all environments, including seawater, acids, and chloride-containing media.

Alloy 718 has much higher strength, with aged tensile strength exceeding 1,240 MPa compared to 827 MPa for Alloy 625.

Alloy 625 is preferred for sustained service above 650°C because Alloy 718's strengthening precipitates degrade above this temperature.

Alloy 625 exhibits better weldability and can be used in the as-welded condition. Alloy 718 requires careful welding procedures and generally needs post-weld heat treatment.

Alloy 718 is generally less expensive due to higher iron content and lower molybdenum content. Alloy 625 costs approximately USD 40-60/kg, while 718 costs approximately USD 30-50/kg.

Alloy 625 is the preferred choice for seawater due to its exceptional pitting and crevice corrosion resistance (PREN > 50).

Alloy 718 is the dominant material for high-stress rotating parts like turbine discs due to its ultra-high strength at temperatures up to 650°C.

No. Alloy 625 is not age-hardenable and is strengthened only through solid solution strengthening and cold working.

Please provide the application, operating temperature, chemical medium (if corrosive), required strength, and whether welding is involved. Our team can provide expert guidance based on your specific service conditions.